1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a semiconductor device having a planarized interlayer insulator film between, beneath, or above metal wirings, and a method of manufacturing the same.
2. Description of the Background Art
In these few years, reduction in the difference in underlayer level and planarization of an insulator film between wirings have become one of the most critical processes in improving the yield and reliability of semiconductor devices corresponding to increase in the density and integration thereof. One of such processes includes the step of depositing a film by a spin-on-glass method with silicon polymer (referred to as "SOG film" hereinafter) and applying a thermal treatment.
The material to form an SOG film (referred to as "SOG material" hereinafter) is classified into two types, i.e., inorganic SOG material, and organic SOG material having a structure in which an alkyl group is directly bonded to silicon.
When difference in underlayer level is to be reduced using an inorganic SOG material, a step of applying an inorganic SOG film 5a on an underlying oxide film 4 as shown in FIG. 24, and a step of applying again an inorganic SOG film 5b for the sake of planarization as shown in FIG. 25 are required. The inorganic SOG film filling the space between the stepped portion receives a tensile stress due to shrinkage of the film at the time of film growth to result in a generation of a crack 20.
When an SOG film is used as a part of a passivation film on a metal wiring, this crack will adversely affect the moisture resistance. For example, a crack 21 is easily generated beneath the stepped portion of a silicon nitride film 11 formed on a metal wiring by plasma CVD as shown in FIG. 26. Although SOG film 5b is applied over the stepped portion, generation of another crack 20 in this SOG film 5b will degrade the moisture resistance in addition to crack 21 in silicon nitride film 11 to result in corrosion of metal wiring 7.
In contrast, there is an advantage that difference in underlayer level can be reduced by virtue of using an organic SOG film 5c as shown in FIG. 27 since a film of approximately 1.5 .mu.m in maximum thickness can be formed just by one coating.
This organic SOG material includes alkyl groups such as Si--CH.sub.3 and Si--C.sub.2 H.sub.5, which can be easily damaged by oxygen plasma. There is a problem that dry etching 22 occurs when a crack or peeling 23 of the film is generated in an etching step of a via hole as shown in FIG. 28.
A structure in which organic SOG film 5c is not exposed at the side surface of a via hole is therefore required. More specifically, overall etchback is carried out after applying a coat of organic SOG film 5c to remove the organic SOG film above the stepped portion as shown in FIG. 29. A structure in which organic SOG film 5c is not exposed at the side surface of a via hole is possible as shown in FIG. 30 by this additional process.
An inorganic SOG film that can be formed in greater thickness than a conventional inorganic SOG film (referred to as "thick-film inorganic SOG film" hereinafter) is a new material for solving the above-described problems of conventional SOG film. Japanese Patent Laying-Open No. 5-121572 discloses an example of the material of a thick-film inorganic SOG film according to the formula of: ##STR1##